Adjustable resistance unit



22, 1931. D, GM 1,838,037

ADJUSTABLE RESISTANCE UNIT Filed May 23, 19:50

IIIIIIHINIH INVENTOR 18 51m 186 H D G 26 iIVl/l/A 4 Q 14AM Patented Dec. 22, 1931 UNITED STATES PATENT OFFICE HAROLD 1). GILL, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOB TO THE UNION SWITCH & SIGNAL COMPANY, OF SWISSVALE, PENNSYLVANIA, CORPORATION OF PENNSYLVANIA ADJUSTABLE RESISTANCE UNIT Application filed May 23, 1930. Serial No. 454,931.

My invention relates to adjustable resistance units. 7

One object of my invention is to provide a resistance unit of the type described having a f minimum number of arts constructed in a Iitl of Fig. 1. Figs. 3 and e are left and right hand end views, respectively, of the resist ance unit shown in Fig. 1. Fig. is an enlarged detail sectional view of the ad ustable contact portion of the resistance unit shown in Fig. 1 taken on the line V-V of Fig.

Similar reference characters refer to s1m1- lar parts in all five views.

Referring to the drawings, the reslstance unit comprises a block 1 of suitable insulating material, such as porcelain, having its sides 2 and 3 tapered to facilitate molding, as best seen in Figs. 3 and 4, and having its ends 4 and 5 provided with projections 6 and 7, respectively. As here shown, the pro ections 6 and 7 are rectangular in shape, but these projections may have any other convenient shape. The sides 2 and 3 and bottom 8 of the block are provided with grooves 9 to receive a resistance wire 10 which is wound around the block to form a. coil in the usual manner. The grooves 9 are so arranged that the successive turns of the resistance wire cross the ungrooved top of the block in parallel spaced relation and at substantially right angles to the longer axis of the block, as best seen inFig. 1, thus allowing a superposed longitudinally adjustable narrow contact 12 to engage each of several adjacent turns at two points, as will beeX- plained more fully hereinafter. The resistance wire may have any desired number of turns, and may be of any suitable size and resistivity, but when the unit is to be used in a railway track circuit, the size and resistivity of the wire will usually be such that a total resistance of about two ohms will be obtained with about twenty-five turns of wire. With this arrangement, it will be seen that the shifting of the superposed adjustable contact 12 the distance between any two turns will cut out of, or cut into, any circuit in which the unit is included a proportionate resistance of .08 of an ohm, thus permitting a comparatively accurate adjustment to be made by estimating the position of the contact along the coil of resistance wire.

An L-shaped support 13 of suitable conducting material is attached to the end 4 of the block 1 by means of a screw 14 located in a longitudinal countersunk hole 15 formed in the lower portion of the block, and this support is provided at its upper ends with two bifurcations 16 which extend upwardly past the opposite sides of the projection 6 to prevent the support from turning. A similar support 17 is provided at the other end of the block 1, this support being formed integral with the lower end of a conducting strip 18 which is attached to the block by means of a screw 19 which extends through a hole 20 in the block 1, and is screwed into a threaded hole 21 in a first vertical portion 18 of the strip 18. The strip 18 also serves as a support for the contact 12 as will presently be described, and for this purpose, the strip is bent to form a horizontal portion 18 which extends along the top of the block in parallelspaced relation thereto, this portion being provided with a full length longitudinal slot 18 as best seen in Fig. 1. The free end of the horizontal portion 18 is bent downwardly to form a second vertical portion 183-, and this vertical portion, in turn, is pro vided at its lower end with a tongue 18 which fits within a slot in a piece 36 of insulating material. The piece 36 of insulating material is attached to the end 4 of the block 1 above the support 13 by means of the same screw 19 which fastens the strip 18 to the block, and is provided at its lower end with an ear 22 which projects between the bifurcations 16 of the support 13 to prevent the insulating piece from turning. The strip 18 is prevented from turning by means of a hole 23 in the vertical portion 18 which receives the projection 7 (see Figs. 2 and 4).

The contact 12 referred to hereinbefore, extends parallel to the turns of the resistance wire 10 where they cross the top of the block 1 and, as here shown, comprises a resilient strip of conducting material bent to form two U-shaped contact surfaces 12 and 12, as best seen in Fig. 5. The contact underlies the crossbar of a U-shaped resilient support 24, and is provided with edge flanges 25 which engage the support at its sides to hold the contact in the desired position with respect to the support. Both the contact and the crossbar fit loosely upon the reduced end of an adjusting screw 31, which end is upset to hold the contact and crossbar in place. The adjusting screw 31 extends through the slot 18 in the horizontal portion 18 of the strip 18 with considerable clearance, and is screwed through a centrally located threaded hole 26 in a guide 27. The guide 27 is provided with bifurcations 28 at either side which are bent upwardly past the sides and over the top of the horizontal portion 18 of the strip 18 in such manner that the guide is free to slide along the strip, but is held at right angles to the longer axis of the horizontal portion of the strip. (Fig. 5.) The upper ends of the support 24 extend upwardly between the bifurcations of the guide, thereby preventing both the contact and the support from turning with respect to the guide. The head of the adjusting screw 31 is knurled to facilitate turning of the screw, and the screw preferably carries a am nut 34 which may be tight ened against the strip after the contact has been moved to the desired. position and forced against the resistance wire with the desired pressure, thus holding the contact rigidly in place. The width of the contacting surfaces of the contact, as here shown, is such that the contact will simultaneously engage three turns of wire, thereby providing six points of engagement with the resistance wire, and thus insuring good electrical connection between the contact and the wire. One end of the resistance wire extends through a hole in the support 13 and is connected to this support, preferably by soldering, and the other end of the resistance wire extends through a similar hole 33 in the strip 18 and is soldered thereto. It will be apparent, therefore, that when the contact 12 is moved toward the left as viewed in Figs. 1 and 2, the portion of the resistance wire between the contact and the right-hand end of the unit is short circuited, thereby decreasing the effective resistance which is included between the supports 13 and 17.

The resistance unit may be mounted on any suitable device but, as here shown, it is arranged for mounting on a standard terminal block 36 of the well known form commonly employed for railway signalin purposes. To facilitate mounting the unit on the block, the

support 13 is recessed at its end while the opposite support 17 is recessed at its side, thereby enabling the supports to be inserted between the washers 29 of the binding posts 30 merely by loosening the nuts on the bind ing posts. When the unit is mounted on a terminal block of this type, electrical connection to the unit may be conveniently made by means of the binding posts 30. It will be noted that ample clearance is provided be tween the ends of the unit and the terminal posts to permit the nuts of the terminal posts to be conveniently tightened by means of a socket wrench of the type commonly employed for this purpose.

It will thus be seen that I have provided a resistance unit which is compact, cheap to manufacture, and which lends itself readily to adjustment without opening the circuit in which it may be included.

Although I have herein shown and dc scribed only one form of adjustable resistance unit embodying my invention, it is understood that various changcs and modi tications may be made therein within the scope of the appended claims without de iarting from the spirit and scope of my invention.

aving thus described my invention, what I claim is:

1. An adjustable resistance unit con'iprising a block of insulating material provided with two projections one located at each end of said block, afirst support of conducting material fastened to one en d of said block and provided with means cooperating with the projection on said one end to prevent said support from turning, a coil of resistance wire wound around said block and connected at one end with said support; a strip of conducting material fastened to the other end of said block and provided at its lower end with a second integral support, said strip also being provided with means cooperating with the projection on the adjacent end of said block to prevent said strip from turning, and with a horizontal portion extending along the top of said block in spaced relation thereto, said strip also having a vertical portion 8X- tending downwardly from the free end of said horizontal port-ion and having a tongue formed thereon; a piece of insulating material secured to the first end of said block and provided with an opening which receives said tongue for fastening the free end of said strip to said block, and an adjustable contact member slidable along said horizontal portion of said strip and adapted for engagement with the turns of said coil of wire, the free end of said coil of wire being connected with said strip.

2. An adjustable resistance unit comprising a block of insulating material having two holes extending therethrough from one end to the other and provided with two projections one located on each end of said block,

a first support of conducting material attached to one end of said block by a first screw located in one of said holes, said support be ing provided with two bifurcations which extend upwardly past the projection on said one end to prevent said support from turning, a coil of resistance wire wound on said block and connected at one end to said support, a strip of conducting material having a second support formed on the lower end of a first vertical portion, a second screw extending through said second hole and screwed into said first vertical portion for fastening said strip to said block, said first vertical portion being provided with a hole which receives the projection on the adjacent end of said block to prevent said strip from turning, said strip also being provided with a slotted horizontal portion extending in parallel spaced relation along the top of said block and with a second vertical portion integral with the free end of said horizontal portion and having a tongue thereon, a piece of insulating material attached to the first end of said block by means of said second screw and provided with an ear which fits between the bifurcations on said first support to prevent said piece from turning and with a slot which receives said tongue, and an adjustable contact slidable along the slot in said horizontal portion of said strip and adapted for engagement with said resistance wire and provided with means for engaging said strip to lock said contact in an adjusted position,

said coil of wire being connected at its free end to said strip.

In testimony whereof I aifix my si nature.

HAROLD D ILL. 

